One of the central challenges in nanotechnology is the development of flexible and efficient methods for creating ordered structures with nanometer precision over an extended length scale. Supramolecular self-assembly on surfaces offers attractive features in this regard: it is a ‘bottom-up’ approach and thus allows simple and rapid creation of surface assemblies (De Feyter & De Schryver, Chem. Soc. Rev., 2003, 32, 139-150; Barth, Annu. Rev. Phys. Chem., 2007, 58, 375-407) which are readily tuned through the choice of molecular building blocks used and stabilized by hydrogen bonding (Theobald et al., Nature, 2003, 424, 1029-1031; Kampschulte et al., J. Phys. Chem. B, 2005, 109, 14074-14078), van der Waals interactions (Furukawa, Angew. Chem. Int. Ed., 2007, 46, 2831-2834), π-π bonding (Mena-Osteritz & Bäuerle, Adv. Mater., 2006, 18, 447-451; Schenning & Meijer, Chem. Comm., 2005, 3245-3258) or metal coordination (Diaz et al., J. Phys. Chem. B, 2001, 105, 8746-8754; Stepanow, Nature Materials, 2004, 3, 229-233) between the blocks. Assemblies in the form of two-dimensional open networks (Theobald et al., infra; Furukawa, infra; Mena-Osteritz & Bäuerle, infra; Stepanow, infra; Stöhr et al., Small, 2007, 3, 1336-1340; Spillmann et al., Adv. Mater., 2006, 18, 275-279; Lu et al., J. Phys. Chem. B, 2004, 108, 5161-5165; and Stepanow et al., Angew. Chem. Int. Ed., 2007, 46, 710-713) are particularly interesting for possible applications because well-defined pores can be used to precisely localize and confine guest entities such as molecules or clusters, which can add functionality to the supramolecular network.
Another widely used method for producing surface structures involves self-assembled monolayers (SAMs) (Schreiber, J. Phys.: Condens. Matter, 2004, 16, R881-R900), which have introduced unprecedented flexibility in providing ability to tailor interfaces and generate patterned surfaces (Gooding et al., Electroanalysis, 2003, 15, 81-96; Love et al., Chem. Rev., 2005, 105, 1103-1170) But SAMs are part of a top-down technology limited in terms of the spatial resolution that it can usually afford.
Additionally, skills and methodology are known in the art that allow the creation of patterned organic layers on surfaces. These include microcontact printing, proximity printing, e-beam or ion beam lithography, photon-based patterning involving (photo)chemical reactions, and scanning probe lithographies. As with existing SAM methodologies, however, these additional top-down technologies are likewise only able to provide limited spatial resolution and/or are slow serial processes.
J. A. Theobald et al. (in Nature 424, 1029-1031 (2003) and US 2005/0214471 A1) describe the production of two-dimensional nanoscale networks on the surface of a substrate formed by deposition of two different types of molecule. The formation of the network relies on the preferential heteromolecular hydrogen-bonding between unlike molecules over homomolecular interactions between like molecules. Resultant pores in the network are described as acting as containment vessels for guest molecules. The networks are described as being prepared under ultra-high vacuum (UHV) conditions (base pressure approximately 5×10−11 torr), a method that is well-known to those skilled in the art.
WO 2008/006520 A2 describes a method for generating supramolecular rotary devices and a supramolecular rotary switch comprising providing a two-dimensional layer of self-organising molecules on an unstructured surface followed by further deposition of additional self-organising molecules/or other functional molecules on the two-dimensional layer, the further deposited molecules accommodating in so-called functional centres of cells defined by the two-dimensional layer. The molecules are described in this publication as having been vapour-deposited under UHV conditions on an atomically clean and flat Cu (111) surface.
Stepanow et al. (Chem. Commun., 2006, 2153-2155) describe the preparation of so-called metallosupramolecular receptors that bind a single or discrete number of cystine, C60 or diphenylalanine molecules in which both the preparation of the two-dimensional metallosupramolecular receptors and the deposition of the guest species are undertaken under UHV conditions.